This invention relates to electrically heated hair curlers and rollers containing as a self regulating heater a positive temperature coefficient thermistor (PTC) material which heats the curler or roller body quickly and maintains the temperature of the roller substantially constant during heating, and to the heater structure in said roller.
Abura et al, U.S. Pat. No. 4,284,877, and Bullock, U.S. Pat. No. 4,447,705, each relate to hair curling rollers having positive temperature coefficient thermistors (PTC) electric heating elements. In Abura et al the hair curler includes a PTC heating element having a temperature self controlling function housed within a substantially hollow hair bobbin. A pair of opposed cup-shaped generally cylindrical members are housed within the bobbin with each cylindrical member including a bottom and a side wall. The PTC heating element is held between the opposed bottoms of the cup-shaped members. A powder supply pin extends through the heating element and both of the bottoms of the cup-shaped members for fastening the heating element and the electrode plates together.
In Bullock the construction is somewhat similar except the bottoms of the cups are held to the PTC heating element not by the power supply pin extending through the heating element but rather, by a number of rivet type connectors extending between the bottoms at the periphery of the PTC heating element. The construction according to the teaching of Bullock requires recesses to be formed in the PTC element and requires the use of many parts thus complicating assembly.